Projects like an annotated bibliography lead you beyond what you knew when you started. Your annotated bibliography will be shaped by what you find and what you've learned, so it make sense to write the Introduction when you know exactly what you've accomplished, and what the final scope and limitations of your resource selection are.
7. Write an Introduction (or an informative Title)
Define the topic, and the scope of your bibliography, whether it is meant to cover the whole range of opinion or just one viewpoint or aspect.
Note: In a very short exercise (e.g.: "Write an annotated bibliography with at least 3-5 different works."), giving it an informative title might take the place of writing an introduction.
For longer bibliographies, especially ones that attempt to give a full overview of a topic, an introduction becomes more necessary. Very specific topics need to be defined clearly, or the reader might be misled.
Describe the scope of your bibliography, i.e. whether it covers what you judge to be the best, or the most recent, or a broad sample of the available material on your topic.
Again, does it cover the whole range of opinion, or just one viewpoint or aspect of the topic?
Example: Postmodern Interpretations of Hamlet
Does it cover a particular time period, or does it reach back for the "classic" articles, no matter if they are decades old?
Black Republicans' Opinions on Barack Obama's First Candidacy for President
Negative Criticism of Keynesian Economics during the Reagan Administration
The Lutheran Response to the Holocaust, 1951-1975